I never finished Ultra, but the consensus I've heard is that normal SuMo has the better story, Ultra has the better postgame content and is at least somewhat more challenging. Which one is better really depends on what you're looking for in a Pokémon game.

$60 is already pushing it for me, anything more and I'm probably not gonna be buying it. Especially when indie games are cheaper, and I tend to like them more than the AAA $60-or-more games anyway.